It has been discovered that there are striking within-species variations in visual capacity among some species of South American monkeys, most notably the squirrel monkey (Saimiri sciureus). These variations include both visual sensitivity and color vision. Thus, it presently appears that as many as six different color vision phenotypes can be found in this species. Of interest is the fact that several of these types are closely similar in nature to the major variant types of color vision in man (i.e., protanopia, deuteranopia, protanomaly, deuteranomaly), and thus this species can serve as a unique biological model for the investigation of normal and defective color vision in man. The long-term objectives of this research are to provide accurate details about the nature of these within-species variations and to discover the biological mechanisms (Photopigment, neural, genetic) that account for these variations. The specific aims of the project are: (1) To further characterize the photopigments underlying color vision variations in primates by making microspectrophotometric measurements on monkeys whose color vision capacities differ in known ways, (2) To develop a noninvasive retinal gross potential measurement (the electroretinogram) so that it can be employed to rapidly and accurately determine the cone photopigment complement of individual retinas, (3) To evaluate through an examination of pedigrees a model for the inheritance of color vision in squirrel monkeys, (4) To examine the organization of the central visual system in conspecifics whose color vision capacities differ in known ways, through single unit electrophysiology and the tracing of projection pathways for color information, (5) to use behavioral tests to determine if other platyrrhine species show within-species variations in visual capacity similar to those so powerfully expresed in squirrel monkeys.